The present invention relates to a process for producing ultra fine silica particles of sub micron size, i.e. silica particles having an average diameter of less than 1 micron. Such particles are sometimes referred to in the art as xe2x80x9ccolloidalxe2x80x9d silica particles.
Ultra fine sub micron silica particles are known in the art. For example, a fine silica particle material wherein the silica particles are spherical particles having an average diameter between 7 and 40 nanometers and produced by the hydrolysis of a volatile silane compound in an oxygen-hydrogen gas flame is available in commerce under the trade name AEROSIL from the company Degussa AG of Frankfurt Am Main, Germany. In addition, the production of fine silica particles is disclosed in xe2x80x9cThe Chemistry of Silicaxe2x80x9d, by Ralph Kìsla, 1979, John Wiley and Sons, Inc. That document discloses on page 25 three ways for producing anhydrous amorphous silica particles at high temperature, these being vaporising silicon dioxide in an arc or plasma jet and condensing it in a stream of dry inert gas; oxidising silicon monoxide in the vapour phase with air and condensing the silicon dioxide; and oxidising silicon compounds in the vapour state, such as SiH4, SiCl4 or HSiCl3 with dry hydrogen or in a hydrocarbon flame.
The present invention aims to provide improved processes for the production of ultra fine sub micron silica particles.
Accordingly, the present invention provides a process for producing ultra fine silica particles, the process comprising directing a plasma jet onto a silicon-containing compound thereby to form silica vapour and condensing the silica vapour on a collection surface.